The technology to prevent the dust derived from powdery material having dusting property is an important technology for daily life and industry from the standpoint of health, safety and environmental issues.
Japanese Patent Publication SHO 52-32877 discloses a method for preventing dust derived from dusting materials by mixing the dusting materials with PTFE and subjecting the mixture to compression-shearing at a temperature from about 20 to 200° C., thereby fibrillating the PTFE to prevent dusting of the powdery material.
The PTFE disclosed therein includes fine powder or emulsion form of homopolymer of tetrafluoroethylene denoted by TEFLON (registered trade mark) 6 or TEFLON (registered trade mark) 30, and also fine powder form of modified polymer of tetrafluoroethylene denoted by TEFLON (registered trade mark) 6C.
Japanese Laid-open Patent Application HEI 8-20767 proposes a dust-preventive method having good stability using an aqueous emulsion containing a hydrocarbon-base anionic surfactant of not less than 1.0 wt % of PTFE, and it discloses that the method is effective for cement dust prevention.
The above-mentioned PTFE particles are obtainable by such emulsion polymerization methods as disclosed in U.S. Pat. No. 2,559,752, in which tetrafluoroethylene is charged under pressure into an aqueous medium containing a water-soluble polymerization initiator and an anionic surfactant having hydrophobic fluoroalkyl radicals (called as a fluorine-containing emulsifier hereunder) as the emulsion stabilizer so as to be polymerized to form the PTFE aqueous emulsion. Further an emulsion stabilizer is added to the emulsion to improve the stability.
However, since these dust-preventive treatment agents are used in large quantities in fertilizers, soil stabilizers, soil solidification agents, reclamation materials such as an incinerated ash of coal and the like, and the scope application of dust-preventive treatment agent is expanding, concerns for the environmental impact has been increasing.
Though a surfactant (a fluorine-containing emulsifier) contained in the PTFE aqueous dispersion as an emulsifier is used in polymerization, it is difficult to decompose and causes concerns for the environmental impact. In addition, since such agent is not biodegradable and is classified as environmental pollutants, and it could potentially pollute ground water, lakes, marshes, rivers and the like.
Therefore, the inventors focused intensely on the improvement of a method that effectively prevents dust and can prevent dust without concern for the environmental impact. As the result, the present invention was developed.
Patent Reference 1: Japanese Patent SHO 52-32877.
Patent Reference 2: the Japanese Laid-open Patent Application HEI 8-20767
Patent Reference 3: U.S. Pat. No. 2,559,752.